This could be fixed at a low level, in gtk filechooser for some cases
or in apps. Gnome-vfs should handle that too.

It would be nice if gnome-vfs could handle this in the background, so
coders don't have to worry about uri escaping and normalization at the
same time. (The existing normalization functions have to be used on
unescaped URIs. It's already tricky enough keeping track of gnome-vfs
escaping issues...)